A. Field of Invention
The present invention relates to polymer composite structures. For example, multi-layer films used for heat seaming polymeric sheeting materials or multi-layer films used for heat seaming roof-sheeting materials are described. Also described are composite structures that include molded polymer structures adhered to one another. In a preferred embodiment, a two component polymer composite structure is disclosed, such as a two-layer film structure.
B. Related Art
As discussed below, certain aspects of the invention are directed to multi-layer films. In the past, polymeric roof sheeting materials in the form of single-ply roofing membranes have been used to cover flat rooftops typically found on industrial or commercial buildings, e.g., factories, hospitals, and school buildings. These roof membranes may be applied on roofs in vulcanized form. Owing to the combination of low cost, ease of installation, weather resistance, and good physical properties, ethylene-propylene-diene terpolymer based compounds have been used in single-ply thermoset roof sheeting materials. Those compounds may be vulcanized in large sheets (e.g., 100 ft.×500 ft.) in an autoclave using traditional vulcanizing agents such as sulfur or sulfur donors. The compounds may also be cured using radiation, as discussed in Valaitis et al. (U.S. Pat. No. 4,803,020). When roof sheets are used to cover a large industrial roof, the ends of the sheets are typically spliced together to form a structurally rigid seam. However, after installation, this seam is constantly subjected to adverse weather conditions, such as thermal stresses, high velocity winds, and moisture. One of the problems with using cured elastomeric membranes for roof sheets is the lack of effective adhesion between adjoining sheets.
Efforts to solve this adhesion problem have included the use of contact or pressure sensitive adhesive compounds to provide seams between adjoining sheets. Examples of such compounds include those formulated with neoprene, butyl or butyl type polymers, and tackifying resins. Those compounds, however, provide poor peel strength. Furthermore, they often experience degradation in seam performance at elevated temperatures. Other examples of pressure sensitive adhesive compositions for seaming roofing materials together are adhesives formulated with partially neutralized or unneutralized sulfonate elastomers, tackifying resins, and organic solvents, as discussed in Berejka et al. (U.S. Pat. No. 3,801,531) and O'Farrell et al. (U.S. Pat. No. 3,867,247). Berejka et al. discusses adhesive compounds containing thiouronium derivatives of unsaturated elastomers or neutralized, partially neutralized, or unneutralized sulfonated elastomers including sulfonated EPDM and other ingredients. O'Farrell et al. discusses adhesive contact cements containing partially neutralized or unneutralized butyl elastomers, tackifying resins, and organic solvent mixtures. However, these adhesive compositions suffer from poor adhesive properties and, furthermore, include organic solvents which may run afoul of environmental regulations. Another article used for seaming vulcanized roof sheets involves the use of a “tie layer” material (e.g., tape) that is inserted between the ends of the sheets and seamed in place by applying heat. Valaitis et al. (U.S. Pat. No. 5,260,111) discusses a heat seamable thermoplastic tape for roofing applications. That tape includes a thermoplastics compound, namely high-density polyethylene, ethylene-vinyl acetate, or blends thereof. However, those tapes still provide poor adhesion and poor seam integrity properties. Therefore, a continuing need exists for improved sheeting materials for roofing applications and for other uses.
For additional background, see also WO 00/69963A, WO 00/69964A, JP 06 263935A, EP 462,680, EP 733,476, EP 716,121, EP 672,737, and EP 593,859.